Cabinet cooling

ABSTRACT

A novel electronics cooling method and system is disclosed. A very flexible and efficient operation of an electronics cooling system ( 10 ) is achieved by controlling circulation of a cooling medium in a closed system ( 40 ) containing an evaporator ( 13 ), a condenser ( 14 ), an ejector ( 11 ) and control valves ( 15–18 ). Specifically, the system is continuously allowed to operate in the most appropriate mode by controlling the valves ( 15–18 ) of the system ( 10 ) based on detected heat load and/or detected heat transfer conditions. By automatically adapting the mode of operation of the system based on the actual prevailing conditions, a unique flexibility is obtained with regard to the cooling mode in which the system will be operated. This means that the cooling capacity will be constantly optimized and that the investment cost as well as the cost for operating the system will be reduced compared to known systems having equal maximum cooling capacity.

TECHNICAL FIELD

The present invention generally concerns methods and systems for coolingcabinets containing heat producing electronic equipment.

BACKGROUND

An important factor in the design of hardware, is the provision ofadequate cooling of the electronic components employed therein. This isespecially the case when designing hardware for use within the modemtelecom and datacom industries. In this area it is an absoluterequirement that the electronic components that are normally integratedin a cabinet are maintained at normal temperatures. Failure to do sowill at least impair the operation and/or functionality of components oreven cause them to fail completely.

Additionally, energy consumption during the life cycle of electronicproducts has the most important environmental and economical impact.Lower energy consumption is a strong sales argument and will be evenmore important in the future. Energy cost for cooling the electronicsduring ten-fifteen years is comparable with the unit's purchase price.The ability to keep the temperature of components at the permissiblelevel is a main reason for thermal management. Up until now, telecomcabinets have been successfully cooled by means of forced air cooling,which is a well proven and reliable method that has been used for manyyears to maintain acceptable temperatures. However, the forced aircooling method suffers from inherent limitations. One such limitation isthat the forced air cooling apparatus of today cannot normally handlemore than a maximum of approximately 3–5 kW power dissipation percabinet, depending on the size of the cabinet and/or the power density.In the new generations of telecom and datacom equipment, higher levelsof heat flux will make the air cooling methods quite inadequate and willrequire more efficient cooling solutions. The next generation systemswill be further miniaturized, leading to higher power density.Furthermore, they will be higher speed systems with increased power andcapacity/performance. All this adds up to increased power dissipation inthe form of heat that needs to be handled. Especially for outdoors RadioBase Stations (RBS), other alternative cooling system must be used, e.g.liquid cooling units.

In order to be able to remove heat in the excess of 3–5 kW per cabinetother traditional cooling methods will normally be recommended, such asliquid cooling with or without phase change, thermosyphon or compressorcooling. Thus, it is well known within the art to use traditionalcompressor cooling systems for cooling air that is in turn used to coolthe electronic equipment, such as for in-house telecom and datacomsystems. Such electronics cooling systems are in essence based oncompressor air-condition systems that are quite expensive and require agreat deal of energy, which also is negative from the environmentalpoint of view. Expressed otherwise, the compressor cooling systems havethe disadvantage of a low overall coefficient of performance.

Among other frequently used methods of cooling cabinets containing heatdissipating electronic equipment shall be mentioned thermosyphoncooling, having the advantage of requiring no additional energy for itsoperation. However, today's thermosyphon systems are rather expensive,at least in relation to their limited capacity when it comes to higherheat loads and/or higher ambient temperatures. Further alternatives thatare used for cooling equipment containing heat dissipating electronicequipment, such as lasers or magnetic cameras, are i.e. liquid metalcooling and cryogenic cooling.

RELATED ART

A system related to the traditional compressor refrigeration system isthe ejector type refrigeration system employing an ejector in the placeof the compressor. This system ranges back all the way to the 19^(th)century when it was used in combination with the steam engine, sincethis system traditionally can make use of waste heat as drive energy, inorder to lower the costs. For the same reason it has been frequentlyused as heat pump in combination with solar energy facilities as well asfor air conditioning systems in automobiles. A common problem with allsuch ejector refrigeration systems has been the poor heat factor of theejector heat pump, resulting in a likewise poor performance. However,lately much research has been performed with the aim of designing moreefficient ejectors intended for use as heat pumps in air conditionersfor buildings. So far no real breakthrough has been made and many knownejector systems are designed to be operated by waste heat, such asexcess heat from solar energy facilities, and to operate at supersonicspeeds. One example of such efforts is known through U.S. Pat. No.5,647,221, directed to what is referred to as a pressure-exchangeejector—contrary to a conventional steady-flow ejector—that allegedlyprovides clearly improved performance. A major drawback of this solutionis the increased complexity of the ejector having moveable parts, namelya miniature rotor intended to perform the actual pressure exchange.

SUMMARY

The invention overcomes the above problems in an efficient andsatisfactory manner.

A general object of the invention is to provide an improved method ofcooling a cabinet containing heat dissipating electronic components. Inparticular, it is an object of the invention to provide a cooling methodbeing able to handle high heat loads very efficiently, at comparativelylow cost and with minimum power consumption.

Briefly, the above object is achieved by controlling the circulation ofa cooling medium in a closed system containing an evaporator, acondenser, an ejector and control valves. Specifically, this object ofthe invention is accomplished by providing controlling the valves of thesystem based on a detected heat load in the cabinet and/or on detectedheat transfer conditions, thereby continuously allowing the system tooperate in the most appropriate mode. Expressed otherwise, the inventionprovides an automatic adaptation of the mode of operation of the systembased on the actual prevailing conditions, so that a unique flexibilityis obtained with regard to the cooling mode in which the system will beoperated. This means that the cooling capacity will be constantlyoptimized and that the cost, both with regard to the investment and tothe operation of the system, will be reduced compared to known systemshaving equal maximum cooling capacity.

During moderate heat load conditions and normal heat transfer conditionsthe system will be automatically controlled for optimum performanceunder those detected conditions. Specifically, in this case forcedcirculation of the cooling medium is interrupted and the appropriatevalves are set in a closed or open condition, respectively to place thecooling system in a “thermosyphon” cooling mode. In this thermosyphoncooling mode cooling medium is allowed to flow from the condenser to theevaporator where the cooling medium is vaporized, and vaporized coolingmedium from the evaporator is allowed to flow to a secondary side of anejector and freely back to the condenser. No external power is consumedby the system in this cooling mode.

Another mode of operation of the cooling system is automaticallyinitiated under detected higher heat load conditions. In this case, thesystem is shifted to a combined liquid cooling with phase change formaintaining optimum performance under the changed conditions. Coolingmedium is allowed to flow from the condenser to the evaporator andforced circulation of the cooling medium is now activated to pumpcooling medium from the evaporator to a primary side of an ejector andback to the condenser. The power consumption for the forced circulationis in this case very reasonable in relation to the total cooling load.

When detecting heat load conditions near or at a maximum a control unitinitiates a further mode of operation. Such conditions will causeautomatic activation of an ejector cooling mode comprising vacuumcompression by means of an ejector. Once more, this will maintainoptimum performance under the changed conditions. This cooling mode willcomprise forced circulation of the cooling medium and will allow arestricted flow of cooling medium from the condenser to the evaporatorwhere the cooling medium is vaporized. The restricted flow is controlledbased on the detected conditions, allowing the remainder of the coolingmedium flow from the condenser to be circulated to a primary side of theejector under a low positive pressure. A negative pressure is created ata secondary side of the ejector to pump vaporized cooling medium fromthe evaporator for condensation. In this way a very cost effectiveoperation of the cooling system will be achieved through low energyconsumption as well an extended optimization of the system performance.

In accordance with further embodiments of the ejector cooling mode thepressure delivered by the forced circulation is controlled based on thedetected conditions, and a pressure difference and a temperaturegradient between evaporator and condenser are regulated by controlling arestrictor valve providing the restricted flow from the condenser to theevaporator to continuously provide optimal cycle conditions.

By the employment of a specific low pressure ejector vaporized coolingmedium is compressed and partly condensed in the ejector beforereturning to the condenser for further condensation.

Another object of the invention is to provide an improved system forcooling a cabinet containing heat dissipating electronic components. Inaccordance with the invention, this further object is achieved by meansof a unique cooling system comprising a closed fluid system connecting acondenser, an evaporator, a fluid circulation means and a low pressureejector through a series of controlled valves. The system furthercomprises a control unit for continuously controlling the positions ofthe valves in dependence on the prevailing operating conditions detectedby temperature sensors.

These and further objects of the invention are met by the invention asdefined in the appended patent claims, in which further preferredembodiments of the different aspects of the invention are alsospecified.

The present invention provides essential advantages over the state ofthe art by providing a cooling method and system that is:

-   -   Extremely flexible by providing continuous automatic shifting        between different cooling modes being optimized for the        different operating conditions:    -   Very cost effective and also environmentally friendly by being        energy-saving and allowing the use of e.g. water or alcohol as        working medium;    -   Fully operable using simple control; and    -   Optimally adapted to electronics cooling; e.g. by providing    -   Good possibility for redundancy.

Other advantages offered by the present invention will be readilyappreciated upon reading the below detailed description of embodimentsof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, maybest be understood by making reference to the following descriptiontaken together with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of an embodiment of the coolingsystem according to invention;

FIG. 2 is a schematic illustration of the embodiment of the coolingsystem according to FIG. 1, operating in a thermosyphon mode;

FIG. 3 is a schematic illustration of the embodiment of the coolingsystem according to FIG. 1, operating in a liquid cooling mode;

FIG. 4 is a schematic illustration of the embodiment of the coolingsystem according to FIG. 1, operating in an ejector cooling mode;

FIG. 5A is a schematic illustration of a practical embodiment of thecooling system of the invention, shown in the ejector cooling mode ofFIG. 4;

FIG. 5B is a schematic illustration of a further practical embodiment ofthe cooling system of the invention, shown in the ejector cooling modeof FIG. 4;

FIG. 6 illustrates an embodiment of an ejector for use in a coolingsystem according to the invention; and

FIG. 7 is a schematic illustration of a theoretical heat and masstransfer balance by a further embodiment of the cooling system accordingto the invention, when operated in the ejector cooling mode.

DETAILED DESCRIPTION OF EMBODIMENTS

The basic principles of the invention shall now be described by means ofan embodiment of a cooling system 10 for performing the suggested methodof cooling a cabinet 50 containing heat dissipating electroniccomponents. The electronic components may be in the form of printedboard assemblies PBA, see FIGS. 5A and 5B, or others. Within thisspecification the expression “printed board assembly” refers to aprinted circuit board with modules and/or components mounted thereon.The general layout of said system is schematically illustrated inFIG. 1. The cooling system 10 is closed or hermetic and filled with aliquid cooling medium that may also be referred to as a refrigerant.Suitable cooling mediums for use with this system are e.g. water,alcohol, ammonia, benzol or other environmentally friendly medium havinga vaporizing temperature of 25–100° C. at a slight subatmosphericpressure or at atmospheric pressure.

The system comprises a condenser/heat exchanger unit 14 provided outsidethe cabinet 50, an evaporator 13 provided in the cabinet 50, a standardfluid pump 12 and an ejector 11, being mutually connected through abasic fluid line system 40. Specifically, the fluid line system 40connects an outlet side of the condenser 14 with an inlet side of theevaporator 13 and with the inlet or suction side of the fluid pump 12 bymeans of separate fluid lines 41 and 42, 45, respectively, and throughfirst and second controlled valves 18 and 17, respectively. The outletside of the evaporator 13 is connected to a secondary or passive mediumside 27 of the ejector 11 and to the fluid pump 12 inlet side by meansof separate fluid lines 43 and 44, 45, respectively, and through thirdand fourth controlled valves 15 and 16, respectively. The outlet orpressure side of the fluid pump 12 is connected to a primary or activemedium side 22 of the ejector 11 by means of fluid line 46 and theoutlet 29 of the ejector 11 is connected to an inlet side of thecondenser 14 by means of fluid line 47. Fluid line 46 is incommunication with a safety valve or expansion tank 9.

The valves 18, 17, 15, 16 are all controlled via a control unit 19 basedon temperature readings T₁, T₂ and T₃ supplied to the control unit 19from temperature sensors 30, 31 and 32, respectively, detecting theevaporator, condenser and ambient temperatures, respectively. Thecontrol unit 19 and the specific control equipment used therein are notdisclosed in detail since the design of an appropriate control unitserving the purposes of the invention lies within the skill of theordinary practitioner. The second, third and fourth valves 17, 15 and 16are directional valves that are normally operated between fully open andfully closed positions. The first valve 18 is a one-way restrictor orthrottle valve being controlled to allow a variable flow of coolingmedium from the condenser 14 to the evaporator 13 but blocking backflowfrom the evaporator 13 to the condenser 14.

Embodiments of the evaporator 13 or evaporator chamber will be describedfurther below with specific reference to FIGS. 5A, 5B and 7, whereas apreferred embodiment of an ejector 11 for use in the system 10 will bedescribed in detail with reference to FIG. 6. The condenser 13 and itsassociated heat exchanger, not shown, are preferably based onconventional technique and their specific design will not be disclosedin detail.

The general operation of the system 10 will now be described. Coolingmedium is circulated in the hermetic fluid line system 40 to absorb heatin the evaporator 13 and to transfer the absorbed heat from the cabinetand to emit said heat in the condenser/heat exchanger 14, as is quiteconventional. However, the invention provides a novel electronicscooling with increased efficiency, reduced energy consumption and alsowith a higher level of functionality. This is achieved on the one handby the unique provision of the evaporator 13 in the cabinet 50,immediately adjacent the heat generating components, and on the otherhand by operating the described cooling system 10 in accordance with acombination of different modes that are based on separate coolingmethods operating according to principles that are known in themselves.Specifically, this is achieved by detecting the evaporator temperatureT₁ inside the cabinet 50 to determine the heat load on the system 10 andby also detecting the ambient temperature T₃ and the condensertemperature T₂ to determine the conditions of the heat transfer from thecooling medium to the surroundings or through the heat exchanger, notshown. The circulation of the cooling medium is controlled based on thedetected heat load and the detected ambient temperature and heattransfer. The flow of cooling medium from the condenser 14 and back tothe evaporator 13 in the cabinet 50, after transfer of heat from thecooling medium, and activation/deactivation of a vapor compression cycleperformed by means of the ejector 11, is likewise controlled based onthe detected heat load and the detected ambient temperature and heattransfer conditions. This method provides for a controlled shiftingbetween cooling of the cabinet in a thermosyphon cooling mode, a liquidcooling mode or an ejector cooling or heat pump mode.

A discussion of the suggested inventive method of operating the systemin either of three main modes of operation follows below. The operationin the three modes, namely the thermosyphon cooling mode (FIG. 2), theliquid cooling mode (FIG. 3) and the ejector cooling mode (FIG. 4) isillustrated in FIGS. 2–4, where arrows CMF indicate the cooling mediumflow in the different modes.

During moderate cabinet heat load conditions (FIG. 2) and normal heattransfer conditions, when the evaporator temperature sensor 30 detectsan evaporator temperature T₁ below a set first level and the ambienttemperature sensor 32 detects a temperature T₃ below a set level (suchas below approximately +30° C.), the control unit 19 will automaticallycontrol the system 10 for optimum performance under the detectedconditions. Specifically, in this case the control unit 19 will stop thefluid pump 12 to interrupt the forced circulation of the cooling medium.Simultaneously, the valves 16 and 17 are closed, whereas valves 15 and18 are set in open condition to place the system 10 in a “thermosyphon”operation mode. In this thermosyphon operation mode, the first valve 18is open for transporting the cooling medium from the condenser 14 to theevaporator 13 but is closed in the opposite direction.

The full flow of the cooling medium from the condenser 14 outlet side isreturned to the evaporator 13 where the cooling medium is vaporized ate.g. 50° C.; and the full flow of vaporized cooling medium from theevaporator 13 is conducted to the secondary side 27 of the ejector 11,through the ejector and from an ejector diffuser outlet 29 back to thecondenser 14. Since the forced circulation of the cooling medium isstopped, no primary cooling medium enters the ejector 11 and no vaporcompression is performed therein. Instead, cooling medium vapor/gas fromthe evaporator 13 drains freely through the ejector. In the condenser14, the transferred vapor condenses at roughly the same temperature(e.g. 50° C.) and the heat is transferred to the surroundings (e.g. theambient air) through a heat exchanger, not illustrated. The temperaturegradient between the surroundings/ambient air and the condenser 14 is inthis case approximately 15–30° C.

The control unit 19 initiates a second mode of operation (FIG. 3) whendetecting higher heat load conditions in situations where theenvironment temperatures are substantially the same. In this case, whenthe evaporator temperature sensor 30 detects an evaporator temperatureT₁ higher than the predetermined first level but lower than apredetermined second level and the ambient temperature sensor 32 detectsa temperature T₃ below the set level, a combined liquid cooling withphase change is automatically activated for maintaining optimumperformance under the changed conditions. The forced circulation fluidpump 12 is now activated to start pumping cooling medium to the ejector11 primary side 22. The power consumption for operating the pump 12 isin this case estimated to be at the most 5% of the total cooling load.

In this mode, the valves 15 and 17 are closed, whereas valves 16 and 18are set in open condition to place the system 10 in a liquid coolingmode. In this mode the full flow of cooling medium from the condenser 14outlet side is returned to the evaporator 13, where a portion of therefrigerant or cooling medium is vaporized at e.g. 50° C. Since the pump12 is activated and the fourth valve 16 is fully open cooling medium andvapor from the evaporator 13 is pumped to the primary side 22 of theejector 11, through the ejector and to the condenser 14.

Since the forced circulation of the cooling medium is activated and theentrance to the secondary side 27 of the ejector 11 is blocked by theclosed third valve 15 the full flow of cooling medium in a liquid and avapor phase is pumped through the ejector primary side 22 to thecondenser 14 where the transferred vapor condenses at roughly the sametemperature (e.g. 50° C.) and the heat is emitted to the surroundingsthrough the heat exchanger. The temperature gradient between thesurroundings/ambient air and the condenser 14 is in this case alsoapproximately 15–30° C.

A third mode of operation (FIG. 4) is initiated by the control unit 19when detecting maximum heat load conditions and/or high ambienttemperatures above the set limit, e.g. 35–50° C. In this situation theevaporator temperature sensor 30 detects an evaporator temperature T₁that is higher than a predetermined second level and/or the ambienttemperature sensor 32 detects a temperature T₃ exceeding the set level.This will cause automatic activation, through the control unit 19, of anejector or heat pump cooling mode in which vacuum compression isobtained by means of the ejector 11. Once more, this will maintainoptimum performance under the changed conditions. The forced circulationfluid pump 12 is activated to start pumping cooling medium to theejector 11 primary side 22. The fourth valve 16 is closed to blockdirect connection between the evaporator outlet side and the pump,whereas the second and third valves 17 and 15, respectively, are fullyopen.

The first valve 18 is operated as a one-way restrictor valve or throttlevalve providing a restricted flow of cooling medium from the condenser14 outlet side to the evaporator 13 inlet side where the cooling mediumis vaporized. Through the control unit 19, the restricted flow throughthe first valve 18 is controlled based on the detected evaporatortemperature T₁ and/or on the detected ambient temperature T₃.

The remainder of the flow of cooling medium from the condenser 14 iscirculated to the primary side 22 of the ejector 11 by the fluid pump 12under a certain positive pressure, thereby creating a negative pressureat the secondary side 27 of the ejector. Since the third valve is open,establishing communication between the evaporator and the ejectorsecondary side, this created negative pressure will cause the vaporizedcooling medium to be pumped out from the evaporator 13 to the secondaryside 27 of the ejector 11. The cooling medium vapor is compressed in theejector 11 through contact with the primary cooling medium flow, as willbe described further below. Part of the compressed vapor condensesinside the ejector 11, at the diffuser 29, and moves directly to thecondenser 14 where condensation of the remaining vapor occurs.

A pressure difference P₁–P₂ (see FIG. 7) and a temperature gradientT₁–T₂, respectively, between evaporator 13 and condenser 14 is regulatedby controlling the degree of restriction of the one-way restrictor 18,to thereby provide optimal cycle conditions in relation to the detectedheat load and ambient temperature T₃. A minor part of the cooling mediumis passed through the restrictor valve 18, being equal to the amount ofliquid that is vaporized. The major part of the cooling medium iscirculated from the condenser 14 via the second valve 17, pump 12 andejector 11 and back to the condenser to create a vapor compression cyclesimilar to that of a heat pump.

The pressure delivered by the fluid pump 12 is also controlled based onthe detected evaporator temperature T₁ and/or on the detected ambienttemperature T₃. By increasing the hydraulic pressure of the pump, theejector capacity to pump out and condense vapor increases. As anexample, the evaporator temperature T₁ is 50° C., and the condensertemperature T₂ is between 55° C. and 100° C. The greater the differencein temperature T₁–T₂, the higher operating power is needed. At smallerheat load and lower environmental temperatures the system willautomatically return to operate in the described thermosyphon or liquidcooling mode.

By means of the invention as described above, it will now be possible tocontinuously adapt the operation of the system to the prevailingconditions. According to the invention, this will be possible with oneand the same cooling unit or system, which may be operated as threedifferent cooling systems. It will be possible to choose the type ofoperation that is most suitable and that may cool electronics with thelowest energy consumption. In other words, the application of thedisclosed features of the invention will not only provide a veryflexible and adaptable cooling solution but will also combine andutilize the best properties of thermosyphon cooling, liquid cooling andejector cooling in one and the same unit. The efficiency of the proposedcooling method and system will be achieved by continuously andautomatically selecting the cooling mode that operates most efficientlyunder the existing conditions. To clarify this a summary of theproperties of the different cooling modes is presented below, inTable 1. For comparison, the corresponding properties of a conventionalcompressor cooling cycle are also given in Table 1.

TABLE 1 Liquid/Water Thermosyphon Ejector Compressor Parameter/propertycooling cooling cooling cooling Heat transfer Maximum Maximum MaximumMaximum 40000 - coefficient, 20000 40000 40000 evaporator; W/(m²K) 50 -air cooling Automatic control Decent Weak Good Poor Power consumption, 5–10 0–5 10–40 20–50 % of cooling capacity Redundancy Decent Weak GoodWeak options Investment cost  6–9 8–10  7–10 10 (Range of 0–10) Coolingmedium 10–20 0–5  0–50 50–80 temperature gradient ° C.¹⁾ External 20 2030–40 30–40 temperature gradient ° C.²⁾ where: ¹⁾= Difference betweenhighest and lowest temperatures of cooling medium. ²⁾= Differencebetween highest temperature of cooling medium and ambient temperature.

Ejector cooling systems are not new as such, but have mainly employedhigh pressure ejectors powered by waste heat or other energy sources.Such systems have been used in particular for air-conditioning units inautomobiles. The suggested introduction of the low pressure ejectorsystem for electronics cooling will provide new functionality forcooling systems that in one and the same system can be operated as athermosyphon cooling system, as a liquid cooling system or as heat pumpcooling system depending on the cooling requirements. For differentelectronics applications, such as for outdoors Radio Base Stations (RBS)and also for in-house telecom and datacom systems the mode of operationthat best suits the prevailing circumstances will be chosen. Forexample, a combination of a liquid and an ejector cooling system or acombination of a thermosyphon and an ejector cooling system, or only anejector system, may be chosen. The final choice criteria should be thetotal cost for the cooling system.

The system provides very flexible control through automatic control ofthe fluid pump and all of the valves. The use of a low pressure ejectorvacuum pump 11 of the design illustrated in FIG. 6 will moreover providea possibility to increase the refrigerating capacity by achieving ahigher heat pump heat factor. Preliminary calculations show thatcompared to a conventional compressor driven refrigerating machine, theinventive system with the low pressure ejector will also be a moreenergy saving solution because of its lower temperature gradient betweenevaporator and condenser. It will also be cheaper and more reliable onaccount of the fact that no rotating parts are used therein. Such asystem using the suggested type of ejector will permit the use of wateror alcohol as working medium, which is very important from anenvironmental protection point of view. As mentioned above, such a useof an ejector system may reduce the temperature gradient betweenevaporator and condenser chambers and reduce both energy and investmentcost for the whole cooling system.

In accordance with one aspect of the invention, a highly efficient lowpressure ejector 11 performs the functions of a conventional vacuumpump/compressor. An example of an ejector of this general design isknown through SU 1714216A1. The employed ejector 11 operates at lowprimary side positive pressure and is schematically shown in FIG. 6. Theejector 11 comprises a main distribution chamber 21 for receiving aprimary or active cooling medium introduced therein through a primarycooling medium supply sleeve 22. In the distribution chamber is provideda multi-channel primary medium nozzle 23 in the form of a sphericalsegment having radial channels or nozzle holes 23A. These nozzle holes23A open into a mixing chamber 24 that is connected to and communicateswith a diffuser 29 through a neck or throat 28. The mixing chamber 24 issurrounded by a secondary or passive medium supply chamber 26 thatcommunicates with the evaporator 13 through a supply sleeve 27. On theother hand, the secondary or passive medium supply chamber 26communicates with the mixing chamber 24 through a plurality of secondarymedium holes 25, provided in a wall 24A of the mixing chamber 24, forthe introduction of the secondary or passive medium. A main feature ofthe ejector device 11 is that the inner cross-section area of the neck28 that conducts cooling medium to the diffuser 29 is substantiallyequal to the total cross-section area of the nozzle holes 23A. Thegeometrical centre C of the spherical segment of the nozzle 23 lies on amixing chamber center axis CA just behind or, expressed otherwise,immediately downstream from the throat or neck 28. The ejector isintended for use with a liquid primary or active medium and a vaporizingsecondary or passive medium. In the embodiments described herein thesame medium, such as water, is used both in the liquid and vaporizedstate.

The ejector 11 works in the following way: Through the primary coolingmedium supply sleeve 22 water is fed into the distribution chamber 21 ata certain positive pressure. The multi-channel nozzle 23 having thegenerally spherical shape and being provided with the small radialnozzle holes 23A, forms a cone of converging jets CMJ as the waterintroduced into the distribution chamber 21 passes through the nozzle 23and into the mixing chamber 24. Water vapor is sucked into the mixingchamber 24 through the secondary medium supply sleeve 27 and supplychamber 26 and the plurality of secondary medium holes 25. Throughinteraction between vapor molecules and water jets CMJ, vapor moleculesbegin to move towards the outlet throat 28 in parallel with the waterjets CMJ. Since the water jets CMJ converge and finally merge, watervapor is compressed and condensed. This means that part of the kineticenergy of the water jets CMJ is consumed to compress and condense thevapor. A main characteristic of the ejector is that it may be operatedboth as a vapor compressor and a condenser. In accordance with theinvention, this characteristic is preferably used in the describedelectronics cooling system. Generally, the inventive ejector coolingmode is optimally adapted to electronics cooling experiencing highertemperatures in the evaporator chamber (up to 65° C.). It providespossibilities for higher temperatures in the condenser (up to 110–130°C. if necessary, but mostly it will be sufficient with 75–80° C. whenthe ambient temperature is approximately 50° C.).

Reference is now made to FIGS. 5A and 5B that schematically illustratetwo embodiments of practical evaporator solutions that may preferably beused in different applications of the system. FIG. 5A illustrates whatmight be referred to as a “direct cooling” evaporator 13 that consistsof several evaporator heat sinks 13A. The heat sinks 13A each directlycontact one or more of the electronic components PBA and preferablyconsist of vertically positioned thin metal plates, e.g. of aluminum,with built-in channels, not illustrated, for cooling medium. In thisembodiment the cooling medium in the channels directly transfers heatfrom the electronic components PBA.

FIG. 5B is a schematic illustration of a “cold wall” evaporator unit113. Here, the evaporator 113 comprises a cold wall 114 containingcooling medium and contacting one edge of several electronic componentsPBA. Transfer of heat from the electronic components PBA to the coldwall 114 cooling medium is performed through heat lines, heat pipes, notspecifically illustrated, or aluminum plates (115). In such a design,evaporation occurs in the “cold wall”.

Finally, FIG. 7 is a very schematic illustration of a further practicalembodiment of the system according to the invention. In accordance withthis embodiment the evaporator 213 has an evaporator chamber 214 and theejector 11 of the system is integrated in said evaporator chamber 214.In a further development, not illustrated, the diffuser 29 of theejector 11 may also be physically connected to the condenser 14 so thatejector, condenser and evaporator chamber are one integrated unit.

In order to provide a presentation of a theoretical heat and masstransfer balance by the inventive ejector cooling system, operation ofthe system will now be described with reference to FIG. 7. As hotelectronic components are cooled, they give off heat Q₁ to evaporatorchamber 214. In an illustrative example, boiling occurs at 70° C. andcondensation at 80° C. A temperature T₁ of 70° C. in the evaporatorchamber 214 should, theoretically, secure the temperature limit of75–80° C. on the pins of components and a temperature of 80° C. shouldalso create a decent condition for cooling the cooling medium in thecondenser 14 (by air heat exchanger at 50° C. ambient temperature). Ifit is possible to store heat in some heat-storing unit (water heater,underground cavity etc.), it is possible to reduce the temperature inthe condenser to 70–72° C. The whole system is filled with water, andhas a pressure of P=0,31 bar.

In a first step, water heats up and starts to boil at 70° C. and at apressure P₂=0,31 bar in evaporator chamber 214. In order to transmitQ₁=2000 W of heat power, an amount M₁ of about 0,9 gram of water persecond should be boiled in evaporator chamber 214. In a second step, inorder to transport vapor (M₁=0,9 gram/s) from the evaporator chamber214, water pump 12 pumps water via ejector 11. In a third step, thegenerated vapor from evaporator chamber 214 is pumped out and condenses,after compression in the diffuser 29, in the condenser 14 under thepressure P₂=0,47 bar and at the temperature T₂ of 80° C. In a fourthstep, water drains back to the evaporator chamber 214 (at M₁=0,9 g/s)from the condenser 14 via restrictor valve 18, and that step completesan ejector cooling cycle.

One of the most important parameters is the coefficient of coolingperformance K=Q₁/P_(el), where P_(el) is the consumed electrical power.The energy needed to power the water pump 12 can be estimatedpreliminary, assuming that the spherical segment of the ejector nozzle23 has 350 radial nozzle holes, each 1 mm in diameter. To reach up to 2m/s of water velocity after the spherical segment, the water pump 12must manage approximately 0,5 kg/s or 2 m³/h. A pressure drop of thesystem is calculated to be ΔP_(tot)=(P₂−P₁)+ΔP_(hyd)=2–3 bar whereΔP_(hyd) is the hydraulic resistance in the pipeline system 40 and theejector 11. To manage that, a water pump 12 having an effect of about500 W will be required. The coefficient of performance can beK=Q₁/P_(el)=2000/500=4.

It will be understood by those skilled in the art that variousmodifications and changes may be made to the present invention withoutdeparture from the scope thereof, which is defined by the appendedclaims.

1. A method of cooling a cabinet containing heat dissipating electroniccomponents (PBA), comprising the steps of: circulating cooling medium ina closed fluid system to absorb heat in an evaporator in the cabinet andto transfer the absorbed heat from the cabinet and to emit said heatoutside the cabinet in a condenser/heat exchanger, detecting theevaporator temperature (T₁) inside the cabinet to determine the heatload on the system; detecting the ambient temperature (T₃) and thetemperature (T₂) in the condenser to determine the conditions of theheat transfer from the cooling medium; controlling a forced circulationof the cooling medium based on the detected heat load and conditions ofheat transfer; controlling the flow of the cooling medium back to theevaporator in the cabinet based on the detected heat load and conditionsof heat transfer; and controlling the activation/deactivation of a vaporcompression cycle based on the detected heat load and conditions of heattransfer; thereby allowing a controlled shifting between cooling of thecabinet in different cooling modes optimized for different heat load andheat transfer conditions.
 2. The method according to claim 1, whereinwhen the detected heat load inside the cabinet is lower than apredetermined first level and/or the detected ambient temperature (T₃)is lower than a predetermined level, a fluid pump is deactivated forinterrupting forced circulation of the cooling medium; the full flow ofcooling medium from the condenser is returned to the evaporator wherecooling medium is vaporized; and the full flow of vaporized coolingmedium from the evaporator is conducted to a secondary side of anejector through the ejector and from an outlet from the ejector back tothe condenser; whereby the cooling of the cabinet is performed in athermosyphon cooling mode.
 3. The method according to claim 2, whereinthe level of the ambient temperature (T₃) is approximately 30° C., inthat cooling medium is vaporized at approximately 50° C. in theevaporator, and in that the cooling medium vapor condenses atsubstantially the same temperature in the condenser and emits heat,whereby the temperature gradient between the surroundings and thecondenser is in the range of 15–30° C.
 4. The method according to claim3, wherein the cooling medium vapor from the evaporator is drainedfreely through the ejector and is condensed in the condenser.
 5. Themethod according to claim 4 when the detected heat load inside thecabinet is higher than a predetermined first level but lower than apre-determined second level and the detected ambient temperature (T₃) islower than a pre-determined level, a fluid pump is activated forperforming forced circulation of the cooling medium; the full flow ofcooling medium from the condenser is returned to the evaporator; andcooling medium from the evaporator is pumped to a primary side of anejector, through the ejector and to the condenser; whereby the coolingof the cabinet is performed in a liquid cooling mode.
 6. The methodaccording to claim 5, the level of the ambient temperature (T₃) isapproximately 30° C. in that a portion of the cooling medium vaporizesat approximately 50° C. in the evaporator and in that cooling mediumvapor condenses at substantially the same temperature in the condenserand emits heat, whereby a temperature gradient between the surroundingsand the condenser is in the range of 15–30° C.
 7. The method accordingto claim 6, wherein entrance to a secondary side of the ejector isblocked and in that the full flow of cooling medium in a liquid and avapor phase is pumped through the ejector primary side to the condenser.8. The method according to claim 7 wherein when the detected heat loadinside the cabinet exceeds a predetermined second level and/or thedetected ambient temperature (T₃) is higher than a predetermined level,a fluid pump is activated for performing forced circulation of thecooling medium; a restricted flow of cooling medium is conducted fromthe condenser to the evaporator where the cooling medium is vaporized,the restricted flow being controlled based on the detected evaporatortemperature (T₁) and/or on the detected ambient temperature (T₃); theremainder of the flow of cooling medium from the condenser is circulatedto a primary side of an ejector by the fluid pump, creating a negativepressure at a secondary side of the ejector; and the vaporized coolingmedium is pumped out from the evaporator to the secondary side of theejector by the created negative pressure and is returned to thecondenser; whereby the cooling of the cabinet is performed in an ejectorcooling mode.
 9. The method according to claim 8, wherein the pressuredelivered by the fluid pump is controlled based on the detectedevaporator temperature (T₁) and/or on the detected ambient temperature(T₃).
 10. The method according to claim 9, wherein the vaporized coolingmedium is compressed and partly condensed in the ejector by the pumpedprimary cooling medium, and is then conducted to the condenser forfurther condensation.
 11. The method according to claim 10 wherein apressure difference (P₁−P₂) and a temperature gradient (T₁−T₂),respectively, between evaporator and condenser is regulated bycontrolling a restrictor valve to provide optimal cycle conditions inrelation to the detected heat load and ambient temperature (T₃).
 12. Acooling system for cooling a cabinet containing heat dissipatingelectronic components (PBA), comprising: means for circulating a coolingmedium in a closed fluid system from a condenser/heat exchanger to anevaporator inside the cabinet and back to the condenser/heat exchanger;at least one valve for controlling the flow of cooling medium betweenthe condenser and the evaporator; an ejector having a primary and asecondary side; a fluid line system connecting the condenser to theevaporator and to a fluid pump, respectively, through first and secondcontrolled valves and connecting the evaporator to the fluid pump andthe ejector secondary side, respectively, through third and fourthcontrolled valves; temperature sensors for detecting the evaporatortemperature (T₁), for detecting the condenser temperature (T₂) and fordetecting the ambient temperature (T₃), respectively; and a control unitfor controlling the positions of the valves in dependence on thedetected temperatures.
 13. The cooling system according to claim 12,wherein the first valve is a one-way restrictor valve blocking backflowfrom the evaporator to the condenser and controlled by the control unitto regulate cooling medium flow from the condenser to the evaporator.14. The cooling system according to claim 13, wherein the ejector is alow pressure ejector operating at low primary side positive pressure andhaving a primary side distribution chamber for receiving the primarycooling medium and a multi-channel nozzle in the form of a sphericalsegment provided with radial nozzle holes leading into a mixing chamberthat is surrounded by a secondary cooling medium supply chambercommunicating with the mixing chamber through a plurality of supplyholes and that is connected to a diffuser through a neck.
 15. Thecooling system according to claim 14, wherein the cooling mediumconducting inner cross-section area of the neck is substantially equalto the total cross-section area of the nozzle holes and in that thegeometrical centre (C) of the spherical segment of the nozzle lies on amixing chamber center axis (CA), immediately downstream of the neck. 16.The cooling system according to claim 14, wherein the evaporatorconsists of several evaporator heat sinks each directly contacting oneor more of the electronic components (PBA).
 17. The cooling systemaccording to claim 16, wherein the evaporator consists of thin metalplates with built-in water channels directly transferring heat from theelectronic components (PBA).
 18. The cooling system according to claim15 wherein the evaporator comprises a cold wall containing coolingmedium and contacting one edge of several electronic components (PBA)and in that heat transfer from the electronic components to the coldwall cooling medium is performed through heat lines, heat pipes oraluminum plates.
 19. The cooling system according to claim 15 whereinthe evaporator has an evaporator chamber, and in that the ejector isintegrated as a unit with the evaporator chamber.
 20. The cooling systemaccording to claim 19, wherein the diffuser of the ejector is physicallyconnected to the condenser.
 21. The cooling system according to claim20, wherein ejector, condenser and evaporator chamber are one integratedunit.